Many implants have been developed to treat intertrochanteric femoral fractures which are basically based on a hip nail or screw that is inserted from the side of the femur through the neck and into the femoral head, and afterwards it is fixed either to an intramedullary nail positioned inside the femoral shaft, or to a side plate positioned in the outside of the femoral shaft.
In 1969 Zickel developed an intramedullary rod and cross nail assembly. U.S. Pat. No. 3,33,220 discloses a hip nail fixed to an intramedullary nail inside the femoral shaft. This device, while permitting an adequate fixation and rotational control of the fracture, was unable to allow sliding of the fracture's bone fragments towards each other along the hip nail. As a result, bone contact was insufficient to support a patient's weight, resulting in an increased risk of bending or breaking of the implanted hip nail. This, together with the shape of the hip nail, determinate too much pressure over the femoral neck and head bone tissue, could lead the implant to cut through the cancellouse tissue of the femoral neck or head in a condition known as “cut out”, causing the nail to pierce the surface of the femoral neck or head, or at the least to lose proper alignment of the bone fracture.
To solve one of these difficulties, collapsible implants where developed. In these kinds of implants, the hip nail or screw is allowed to slide back through a bore in the side plate or intramedullary nail, permitting the migration of the bone fragments into each other, and therefore allowing the reduction of the fracture as the patient ambulates (bearing weight in the fractured limb). This allows for increased bone contact, tolerating more pressure and therefore minimizing the tendency of breaking the hips' implant. An example of these implants is Lawes intertrochanteric fracture fixation device, disclosed in U.S. Pat. No. 5,176,681. However, these implants have a small horizontal surface to contact with bone tissue. Thus, when the healing bone is under the patients' weight, the implant may cut through the cancellous bone of the femoral head, causing the implant to rupture the femoral surface, or to no longer maintain a proper alignment of the fracture. Another disadvantage of these types of implants is that they lack rotational control, permitting the rotation of the femoral head around the hip screw.
Thereafter, complete helical blades were developed, such as Neufelds' Subtrochanteric Nail described in U.S. Pat. No. 4,103,683; and Friggs' Fixation Plate disclosed in U.S. Pat. No. 4,978,349, which consist in a single helical blade that is inserted through the femoral neck into the femoral head, so that when the insertion is completed the distal end of the blade lies in a vertical position passing through a vertical slot in the intramedullary nail; while the proximal end lies in a horizontal position, permitting the load to be dispersed over the femoral head and act on a larger and flat surface. This diminishes the pressure on the bone tissue, thus reducing the tendency of the implant to cut out after implantation. Although this may solve the cutting out problem and achieve adequate rotational stability, this system does not allow the sliding back of the implant through the vertical slot in the intramedullary nail, and therefore fails to permit the necessary bone fragment migration needed to provide fracture compression.
In order to obtain the necessary sliding (minimizing the implants' breaking risk, while permitting compression of bone fragments), and to avoid the cutting-out problem of complete helical implants, partial helical implants were developed. Examples of these implants are the Two-part Angle Plate invented by Frigg U.S. Pat. No. 5,300,074, and Bresinas' Helical Implant U.S. Pat. No. 5,908,422. In these devices the hip implant consists of a proximal helical blade at the front portion of the implant (which increases the surface over which the load acts, preventing the cut-out), followed by a distal shaft at the rear portion of the implant which is able to slide back through the bore in the intramedullary nail or side plate. The shaft needed to permit sliding does not allow rotational control, which may result in the rotation of one bone fragment around another. In addition, partial helical implants have an additional draw-back: the helical implant needs to be inserted in a guided way that permits the implant to rotate in a constant and predetermined rhythm, otherwise the implant would provoke femoral neck and head tissue loss while being inserted, and as a consequence the fracture fixation may become unstable, mainly in osteoporotic bones. Therefore, an outside guide (outrigger) is required to guide the insertion of this partial helical implants. Such a design and use is very complex.
Accordingly, a need exists to develop an osteosynthetic implant to treat intertrochanteric femoral fractures that minimizes the tendency to cut through the femoral head and neck tissue after insertion, that permits sliding, maintaining rotational control; and that has an easy guided insertion, without the need of an outrigger.